This invention relates to an improved multi-frequency antenna system and to an antenna system which is particularly suitable for reception of signals within the high VHF (very high frequency) television frequency band and low VHF television frequency band and to the reception of signals within the UHF (ultra high frequency) television frequency band. These VHF bands cover the frequencies from 54 - 88 megahertz (MHz) and from 174 - 216 MHz. The UHF band covers the frequencies from 470 MHz - 890 MHz. It is desirable that a single antenna system be provided that is effective over both of these VHF television frequency bands and the UHF television frequency band.
One technique for extending the bandwidth of a television antenna system is to provide a plurality of colinear center fed or driven dipole elements with the lowest frequency dipole element located at one end and higher frequency dipole elements aligned and progressing toward the opposite end with the whole system fed at one end. Appropriate spacing is provided between each of these dipole elements and an appropriate feed line arrangement is provided to obtain relatively good reinforcing effects between the separate elements and to provide a relatively good antenna system for the low VHF (54-88 MHz) television frequency band. The appropriate antenna feed arrangement in order to permit close spacing between the colinear dipole elements when feeding at one end of the system requires a transposition of the feed lines between these dipole elements. This transposition of the feed lines is accomplished in one arrangement in the prior art by crisscrossing the feed wires above the boom which results in variations in spacing and in impedance that can degrade the characteristics of the antenna response. Also, in the prior art, this has been achieved by feed lines extending symmetrically on opposite sides of the boom which leads to complex and costly feed line structures for coupling to the dipole elements extending on opposite sides of the boom. Also, in the art, there have been constructed complex support booms which effectively provide two transmission lines. This complex boom structure also leads to high cost in the construction of an antenna system.
As stated previously, it is also desirable that the antenna system be operational over the UHF television frequency band. Since it is desirable that the entire antenna system have but one lead from the television set to the antenna, it is desirable that the entire UHF and VHF antenna system have a single feed point. It is desirable, therefore, that the same feed line for the VHF elements be a continuation of the feed line for the UHF element or vice versa. It is, therefore, desirable that the transmission line feeding the UHF elements match the feed line portion which feed the VHF elements in a manner not to degrade the characteristics of the antenna response in either the UHF or VHF portion. It is also desirable that this manner of achieving match be provided using simple low cost construction.